Emedastine is the generic name for 1-(2-ethoxyethyl)-2-(hexahydro-4-methyl-1H-1,4-diazepin-1-yl)-1H-benzimidazole. Emedastine has a histamine release inhibitory action and an antihistaminic action, and is known as a drug which achieves an antiallergic effect. For example, oral preparations such as capsules containing emedastine difumarate (molecular formula: C17H26N4O.2C4H4O4, molecular weight: 534.56) are commercially available.
However, emedastine has the following problem. Specifically, when emedastine administered orally, the emedastine concentration in the blood fluctuates over a wide range, so that adverse effects such as drowsiness tend to be caused. In addition, for example, Japanese Unexamined Patent Application Publication No. Hei 3-83924 (PTL 1) describes parenteral preparations such as oleaginous ointments, gels, creams, lotions, and sprays using a liquid composition comprising emedastine. However, from the viewpoints of reduction of the above-described adverse effects and improvement of the stability of the drug effect, development of a patch which enables more stable continuous administration of emedastine has been desired.
Examples of patches comprising emedastine include a patch comprising an adhesive layer (adhesive agent layer) comprising an acrylic adhesive base, a silicone-based adhesive base or a rubber-based adhesive base, and emedastine described in Japanese Unexamined Patent Application Publication No. Hei 7-33665 (PTL 2), and a patch comprising an adhesive agent layer comprising an acrylic polymer and emedastine described in Japanese Unexamined Patent Application Publication No. Hei 8-193030 (PTL 3).
When an acrylic adhesive agent is used as the adhesive agent, as described in PTLs 2 and 3, somewhat good transdermal absorption of emedastine is exhibited. However, when a rubber-based adhesive agent is used, there arises a problem of insufficient transdermal absorption of emedastine.
In addition, International Publication No. WO2005/115355 (PTL 4) describes a patch comprising an adhesive agent layer comprising a basic drug such as fentanyl or oxybutynin and a volatile organic acid, and also describes various organic acids and organic acid salts including sodium fumarate as compounds which can be added to promote the transdermal absorption of the basic drug, if necessary. However, PTL 4 does not describe emedastine at all.